It has been known for a long time to reduce the SO2 content and the NOx content of the flue gases from gas turbines to environmentally acceptable values by means of catalyst plants which comprise respectively a so-called SCOSOx catalyst for the removal of SO2 and, downstream of this, a SCONOx catalyst for the removal of NOx. The catalysts are relatively rapid in their effect, and it is likewise known to regenerate them by means of substantially oxygen-free regenerating gas which is passed through them to restore their effectiveness.
Thus the use of a regenerating gas for the regeneration of a SCONOx catalyst is described in U.S. Pat. No. 5,762,885, and the gas contains 4% of molecular hydrogen as the active substance; the rest is a carrier gas, which principally consists of steam and contains small amounts of molecular nitrogen and carbon dioxide. If the regenerating gas is passed only once through the catalyst, a very high consumption results, and correspondingly high costs arise. In the described case, the production of the steam is costly in energy and correspondingly expensive, especially as demineralized water is required for its production. In the above reference, it is also proposed to utilize used regenerating gas as carrier gas. In a closed circuit of regenerating gas through a catalyst plant, which also contains a SCOSOx catalyst, the SO2 released in its regeneration would however poison the SCONOx catalyst.